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TE eRN I CA.T~ IvlElJORA1\j"DLTlIi S
NATIONA~ ADVISORY COMMITTEE FOR AERONAUT lOS
No . 860
TH~ DESIGN OP FLOATS
By W. Sottorf
Luftfahrtforschung Vol . 14 , No~ . 4 - 5, Auril 20 , 1937 Verlag von R . OldenlJourg, lti~!lchen und Borlin
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Washinbton April 1938
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NATIONAL ADVISORY COM~ITTEE FOR AERONAUTICS
.. TECHNIC AL MEMORANDUM NO . 860
THE DESIGN OF FLOATS*
By W. Sottor f
Following a summary of the multiplicity of domestic and. forei ~ n floats and a brief enumeration of the require ments of floats, the essBnt i al form parameters and the ir effect on the qualities of floats are detailed. On this basis a standard f l oat design i s developed which in model families rrith varying l ength/beam ratio and angle of dead rise is analyzed by an expcrime!).tal method I'.hich permits its best utilizat i on on any air plane. A comparison with the bent U.S . N. A. C. A. model No . 35 reveals the quality of the DVL standard float which t among others, is used on the Ha 139 of the German Luft Hansa.
nOTATION
total length of float, (m) .
length of forebod: , ( m) •
~or izontal distance of the c ente r of buoyancy from the steP t (m)
vertical distance of the water line from the bottom of the keel at the step, (m).
b nt , beam of float at the step, (m) .
b nat , natural beam of pressure area , (m ).
h st t clepth of step , (m) . A, lift, (kg) .
w, resistance, (kg) .
3 Dt static displace~ent at rest , (m ) •
------. ------~------*IIGes taltung von Schwimmwerken . III Luftfahrtforschung t vol. 14, nos . 4 -5, An ril 20 , 1 937 , pp . 157- 167 . 2 N . A . C. A. Technical Mornornnduc No . 860
G, gross weig4t.of airplane , ( kg ) •
P, i mpact load , ( kg).
E, unloadi ng , (kg ).
'Y , s:pec i f ic i7e i ght,
Doment about the transve r se axis thr ough the po i nt of the step, (mkg) . v , 8:!?O ed , (m/ s ) • v n D.x ' speed at maxi mum r esistance , v t ~ Got- away speod , (m/ s ) • s a r v t e: = A'IV :!? l an i ng nunber . A C a f = load coefficient . 'Y b 3 st
CODent coeffi cient .
F = -======v , Froude nunber . J g ba t
A, sc~le of nodol . a = tri~ , angle with the horizGntal of the tangent to the keel at the step .
trin of n i n i nun resistance . (:Best tr i m.)
, angle of Ir ing chord to the tangent to the keel CJ 1 at the step .
included angle of dead rise (dihedr a l angl e) . ~J . A . C . A. Technical Lomorund.uJ:'1 No . 860 3
I . 'I'HE FORMS OF DO ME STIC AND FOREIGH FLOAT SYSTE MS
A survey of the type~ of seapl ane dev eloped here ~nd abroad within tho las t yeurs, d i sclose s the v iews of the desiGne r e us regards sui table des i gns and dimensions of float systems a re still g r ently at vari~nce .
Fi ~uro 1 shous that the b eam a t the step bet vers~s g ro ss weight G for fl y ing boats and a gai nst G/2 for tuin-float seaplane s in logarithmic s cale . The load coef G f i cients c t ------n re used as the parameters and, a - Yb 3' s t accordi ng to New ton 1s gene r a l law of s i mili tude, are con stant for simi l arly loaded fl o a t syctems . EstabliGhi~g f with cal = 2 . 92 constant a l oue r, and with ca = 0.364 con ct~nt an upper , l i mi t on the cluster of points, t he reGpe c t ive liJ:'1it ing be ams of fl oat systems that have been ( r1)1/3 ( )1 /3 b u:11 t CJ reb s t = O. 7 \ ~ an d I • 4 ,,~ , an d fo r equ ~ l load , a re in the ratio of 1 : 2 .
Fieure 2 sho~s , to the same scale , midship sections and sheer p l a ns f o r a selection of well- known types wh ich , by applying t his l aw of si milarity , have been reduced to the CO ~Bon gross we i ght of 1 ton for both hulls and float. It illus t rates how different l y beam , l e ngth-beam rat i o, length of forebo dy , to tal l eneth, or p osition of step and cro ss . scction we re se l e c ted by the various designera , and it is not to be assu med t hat these des i g ns are of equal valle. The differ e nces i n fo r m are i n p art conditioned by different requirements of tho float system . So if any standardization of the form of the float system is to be atteMptod, the r equire ments must f irst be defined .
II. REQ.UIRE ENT S OF A FLOAT SYSTE M
a) The wat e r resistance must b e small and the anglo of at tack of the p l an i ng bott om to be reached by pulling up Mus t a t the instant of get - ~TIay , be great enou gh to be abl e to bri ng the angle of at tack of the wing into the range of c . a max 4 N. A. C. A. Technical Memorandum No . 860
The g r eat e r the ~xces s thrus t a nd the lowe r the ge t - array speed , the small e r t he t ake- off t i me and t ake- off run .
b ) The spr ay f ormed shou l d be small.
c ) The i mpact fo r ces excited durin g t ake - off a nd l andi ng s houl d be suall. They i n creas e wi th the seauay , fo r wh ich reason t h e str eng t h spo c i f icat i on s a r c g r ouped ac c ording to s tresscs i n o rde r to b e abl e to mod i f y t h e r e qu irements r e garding sean o r t h i ncss .
d) Duri ng take- off the a irp l a n e mu s t h a v e no t endency to oscillat e abou t t h e t r ans v e r se axis which nay be c ome t h e cause of d e l ay of take- off and of po r p oi s i ng at h i g h e r speed .
e ) Ri ding at an cho r, the a irp l ane should be weat h e rly , so that borr u i l l he~d into t h e wind ; i t fur ther shoul d be s t able about a ll ho rizo n tal axes i n a s i de wi n d , whose v elocity i s in p r opo r tion to the require d seauorth iness . I n twin- float sea p l anes the mi n i mu m s t ability occur s wh e n down by t h e stern , and the r efo r d i s de t e rm i n ed by t he f orn of the float . In f l y i ng b o a ts and sea p l anes with a c e n t r a l float , it oc cur s unde r t r ansve r se i nclination , in wh ich c a s e the s ize and d istan c e of t he side float s a r e de ci s ive .
r ) Wh i le maneuve ring the a irp l ane mu s t r espond qu i ck ~ ly t o a ir and wat e r rudde r s .
g ) The a ir res i stanc e must be sm all .
The effect of the fo r m par amete r s on po i n ts a) t o c) wi ll b e di scussed af t e r the take - off p rocess h a s b een de ~ scr i bed . Data for a qu al i tative opinion r egar d ing p oin t d ) ~ r o a l togethe r l a c k ing at tho p r esen t t i me . Tho char a ct ori sti c s c ited unde r po i n t s 0 ) and f ) a r e l a rge ly de pendent on the a irp l ane des i gn as a wh ol o a n d t h e r efo re wi ll not be d iscussed fur the r in the p r esent pape r .
I I I I I I I ~ . ------~j \
N.A.C . A. Tochnical Memorandum No. 860 5
III . TAKE - OFF WI TH SPECIAL REFERENCE TO
THE EFFECT OF THE AFTERBODY
Figure 3 sho7s a take - off diagram with the usual curves of tho forces and trims . It may be divided into four speed stages , in which the flow forms differ markedly and consequently , the effect of the aft e rbody on the take off is oarkedly different .
EiK.21_1il.s;gg : At the beginni ng of the take-off there is no differen ce hydrodynamically, between planing and displacement craft, since flow is taking place over the limiting edges of the planing bottom at the sides and on the step and t he sides themse l ves are webted . The form of the hull, in itsel f unfavorable, produces a relatively high resistance, wh ose effect on the get- away, however, remains small as this stage is quickly passed through, be cause of the great excess of thrust. At around i v max (the Bpee~ of maxi mum re s istance) the relative speed of t:h·c wa t era t the step is al ready so great that br eak-away takes place . But the trough or wake formed aft of the step is as yet short and the major part of thp afterbody is still in contact with the water . Considoring the water forcos on tho forebody and aft e r body separately (fig. 4), the afterbody carri es almost half the load. Because of tho negative angle of the after body keel, the resultant normel fo rce acting on the afte r body surfaces has a hori zontal component opposite to the resistance of the fore body and lowers tho totnl r esi stance. The resultant of the total w~ter for c es has mo ved foruard but little from its position at rest, so that the trim of the float re mains sT:lall.
£gcong~.21.s;gg : As the i mpact pressure increases, the l ength of t~e furrow aft of the step increases and the contact between the bottom of the afterbody and the water travels correspondingly further aft . The process of gat ting on step is characterized by a sudden emersion of the float occurring withi n a narrow speed range and accompa nied by marked increase in tr i m.
The maxi mum resi stance of the float lies a little higher - usually botween 0 . 3 and 0 . 4 Vstart. Only the af- ter part of the afterbody is then in contact u ith tho wa tor; the sides are co mpletely froe . The aft e rbody, with 6 R.A.C.A. Technical Memorandum No . · 860 i ts share of the lift , tends to decrease the r esistance, ovon at the hump . The re sultant water fo rce h as r eac hed i ts most fo r ~ard posi t ion i n the r ange of maxi mum r es ist~ nnco , n i th ~hi ch monent and trim also reach their mnx i mun values. The tri m i s reduce d n oro o r less by the nosehoavy mo nont of tho afterbody i n the p r oportion that the aft o r b ody shar es in the lift.
T;lO effe ct of the aft or bo dy in stage s I an d I lis such tha t tho curve of tho resistance of a fo r ebody towed wi th out afterbo dy is the envelope of the curves of combinations betweon f o r ebo dy and a f t e rbody . The more favorable the sup!..)ort by the aft e rbody , the lower the hump, which i $ shi ft ed toward h i g her speeds on acc ount of it (and not as a re sult o~ the later fo r mat i on of the p l ani ng condition) .
1hi~Q_~1~€g : The furrow aft o f the step has become so long that the conflux in the p l a ne of symme try of the waves comi ng f ro m the sides of the p l aning b o ttom ~nd bounding the furrow l lies be~ind the float so that the roach fo r med there no longe r str i kes the aft e rbody. I n this stage of pure p laning, the float at normal trim tou c hes the wate r only with a portion of the plani ng bot tom l ying for ward of the step . As the i mpact p r essure i n creases , tho p r essur e area becomes shorter and then , since t he ~ings unload the airpl ane mo r c effective l y , tho re sultant water forco shifts bac kward and the trim o f the float do creases. Towar d the ond of this stage the natural trim of the f loat has continuously decreased to a v e ry small anglo . By i n creased pulling up , the float i s held at a DoQiurn trim, favo r ~ble in r elation to tho total re- s i stan co.
E~n~lh_21~gQ: In the stage b efo r e tho get- away , o on t a ct of the af t e rbody with the wate r spray is unavoidabl e . In a flo~t ~ i th doad rise, the beam of the bottom becomes greator than the natura l beam of the bottom area under pressure be cause of the small load r emain i ng , as a re sult of wh ich a heavy spray e s capes backward ( fig . 5 ) . over the open outer edges of the bot too . To insure a short take off t:1e ai r p l ane must be pulled· up to get-away (a.max = angle of afterbo dy kee l), wh ich i ncr eases the effect of the s pray on the afterbody . The tangential contact of thi s water with the afterbody increases the frictional r e s istance so much t hat unde r c e rtain circums tances the to t a l resistance equ~ ls the propeller thrust despite the small load left on the water and g et- away become s i mpos s ibl e . j N.A.C.A. Technical Memo r andum TI o. 860 9
The control of the p roj ect ed spray takes place in the part of the bo ttom noar the ch i n e s. Syst ematic tests h~v e shown that tho n at e r i s kep t flat when t he section i s tu r~od to the horizonta l, ac cording to figure lIb, with not too small ~ r ndius of c u rva tur e . With a straight soc ti on (fi g . 11a) the wate r r i sos h i g h in continuation of the d. lro ction of t he bottom , uhilo ·with prono1,lnced reeur vatul'e at tho ch i n o (fig. lIe) it i~ d irected against tho s' rfaeo t7ho re it i s refl o cted a t a ~1. i g h angle. Figu re 1 2 sho ~ s tho s? r ay patt e r rr s of a mo del in which tho left half o f the GO c t~on D w~ro curved downward according to figure lIe, uhilo those o f t he ri g~ t half t e r mi nated in the hori zo ntal (fig . lIb) . The di fferen ces in the fo r m of the s~ray oro roadily a een. A r o curvature at t ho chine that goee b o~ro nd tho horizontal , hac a v e ry unfavorable effect on landi nc sho ck (refe r e nce 4 ) and is thorofore to b e avoided.
LonGitudinal s t eps of ov o r y k ind have proved unsuit able in syetematic tosts of p laning surfa ce s and models with rospect to r es i s t an c e ; no ithor do they offe r a ny ad v ~ nta~oB rol~t ive to imp~ ct forces.
Do~th nnd Location of Step ; An g l e of Afterbody
Tie locati on o f a straig ht af t e rbody r elative to the furroIT fo r med aft of the step is dete r mined by the depth of step an d the a~glo b e tueen forebody ~nd afterbody .
It h~ s b een esta~ li shed t hat contact o f the stern ~ i th tho solid wat e r behi nd the furrow at maximum resist ance h~B a favorable e f fe ct, ITh ilo contact of the stern '.7 i tIl t:lO spray in J~he stage befo r e g et- away has an advorne offect.
At max i rn un resistan ce , tho refore, small depth of step and sDall angle bett7c e n fore b ody and afterbo dy are adv~n tage ous , uhilo just befo r e ge t-aua y g r eat depth of s top and l arge a n g l e of aftorbody keel (forobody. a lone: opti mum) 0ro adv on tage ous as s eo n in f i gure 1 3 , t7h ich presonts tho resu lts o f modal t ost s u ith.differen t depths of step ~nQ <:',nglos of aft e r body . Tho r esults fro m tho forebody aro appended as lin i t i ng v a l ues . 10 n . A. C.A. Te chnica l Mem orandum No . 860
afterbody k eel
II
" 0 . 3 VB c 0 . 05 " 0 " 3 VR d " VB e II 0 . 3 V ---- -.._------_I.,
T~ c expected decr ease i n resista nce from the flo ~ t u ith ~ ro ~ ter dopth of step (limit va lue : fore b ody alono) to the float u ith ze r o d epth of step appears i n the stage be : o re tho maxi mu m.
At max i mum re s istan ce the conditions on the stepped float are as ye t the same . But fo r step depth 0 , i t ap pea Te that t he a ir apace in c ourse of fo r mation behin~ tho b reak is filled u p a gai n f r om the r oar, so that the ge t t i ng- o n- step is g r eatl y retarded and the maxi mum re s i ctance, as a result, increases furthe r . Even if by fur the r i ncrease of speed, t he p l a ning condition has been ren c he d the r e sistances are from t uo to three times as h i gh a s fo r the stepped flo~ts .
In the stage before g et- n:rray the float wi th the great est depth o f s top (or the forobody alone ) shoTIs the low est r os i stanc o , while the float TI it h zero depth of stop i s ~lt o gethe r unusable .
A depth'o f step of f ro m 0 . 04 to 0 . 05 b st ha~ proved s a tisfa c t ory . On h i gh- speed a irp l anes , it is reduced to 0 . 025 b s t i n o rder to r oduc o the a i r resistance .
Tho m~x i mum r es i s t anco be comes g rea t e r u ith large an g l OD of af t e rbody keel, uh i ~e the spr ay effect falls short l y befo r e ge t - auay nnd thr ough it, the rise of resistance occurri ng thoro, i s reduced.
Be cause of the dependen c e o~ t h e f orm of uake on dead I I ri se , load, and speed , no gener a lly valid statement c an be I mado rc g~rd in g the opt i mun angle between af t e r body and I fo r oD o dy ; 7 0 h~s p roved to be a good a v e r age va lue . I I I I I ~J B .A.C.A. Te chnical Memornndum No . 860 11
N~tur~l ly, the ~ r guD8nts refor to the ratio:
!~~~~~~~_~~=~~~_ 1v def i n i ng the location of the step . over-~ll l~ngth 1L'
With decre~s in g 1v/1L' the f~ vor a ble effect of the ufter- body In crc~s e G in stage s I a nd II, ~h il e in stage IV, ~ larGe 1v/tL is desired , in o rder to r oduOe t he ~rea of the ~fterb o dy h it by the op r ay . tv/tL = 0 . 55 i s a good v alue for f loets . For flying bOats having aft of the sec ond atep ~ t~il extension ~ it h l~rg c r auele of keel , the length of the afterbody (~eaBured to the second stop) may (,V be shortened to about -- = 0 . 65 to favor tho forebody, 1 L if otage IV noe ds a reduction in re s istance, inasmuch as tho tail oxtension insures am ~ le stability by the stern. 1v/1t is the only parame ter wh ich, unde r c ertain condi- tions, causes a diffe rentiati on b e tw een float and flying boat hull.
V. THE DVL STANDARD FLOAT
The DVL standa rd float - a floa t design evolved on the forego ing ~ rgument s - is IBrgely patterned after proved desi gn fo rms based urou ton ye rs l oxperie nco , not only in problems of ros ist ~ nce but a lso i n n roolems of strength, as well as mot ion charact e ristics . Needlessly complicating deteils, which now ~nd a~a in nppear in a s ingle develop ~ ment not - or only parti n. lly - ut i lizing the po'ssibilit ics of the research , have beon left out .
The need fo r being able to vary the lengt h-be um ratio tL/o s t and tho included ~ng l e of doad rise t, to suit ~ particul~r purp se, l eads to f~m ili e s of related floats , for which the i nvest i g ation must be made on such a wide r anbe of selected loads , t rims , and speeds that for e v ery suitable p osi t i on dete r mine d in c onjunct ion with an air fo il, the test values can be obtai ned by i nterpolation within the curve sy s t em , providi ng that no stages already de f ined by limit i ng cur v es are reached in which the f l oat becomes unsui t able with respe c t to resistance or spr ay formation . The be nt c oo r d ina tion of the float system to the a irfoi l of the p rojoct follows on the basis of the measurements . This method was suggested by Seewald (re f erence 5) used in the P .A. C. A. tank (rofere nce 6), and further develope d by th e DVL . 12 R.A. C. A. Technical omorandum No . 860
Th~ des i gn of tho s i x mode l s investigated so far :
1, L/ 0 s t ------6 . 04 0 tt.19 Family A: ~ = 140 Mod el la 8 7
0 \I B: ~ = 130 \I 17 18 19 is shown i n f i gure 14. The beam of the model i s b st = 0 . 3 m. T_le mode l s of a fam ily a r e developed from the oasi c fo r m ( smallest 1 1 /bst ) ' by s t a rting at the step and increasing the spac i ng of the section s of the fore body and afte r body along the keel t a n gen t in the ratio to the nodel lengths . Depth of step and angl e oetwee n fo re body and af t e r bo dy r emain constant fo r all mode l s . The rel-:1t ed mode ls of the tTIO famil i es D. r e cong ruent i n ccm tar-line se c tion and plan. The v e rtica l depths of sec tion (measured fr o m oase of section ) are to one anothe r as 1 80 - ~ the dead ri ses t an ---~---.
The modele hav e vertical s i des and str a i ght deck . No attempt ~as made to gi v e the upper part o f the float a speci~l fo r m, s i nce discrepan cies in the fo r m of the sides can infl uence the test data only at the begi nn i ng o f the t~ke -o ff and o ven thon, onl y to a negligibl e ex ~ent. The fo r m of the u pper part i s loft to tho con structor .
VI. METH OD OF TOWING
The ranges i n TIh ich ~ float system i s to be i nvesti gated ~re set off :
1) The speed range is given by the Froude numoe r F ' = 10 , corresponding to an aesumed high take-off speed ;
2) T~c lo a d r ange : The load limit depends upon t he length-oeam ratio . It lies at a round ca l = 3 for slen- der floats . The program of i nvest i gation c ontempl ates an increase of the test points at h i gh loads i n the zon e of max i mum resistance; in contrast , the small loads a r e in vestigated only in the upper speed range . As the i nvest i gation proceeds, it can be seen in what d irect ion the N.A.C . A . Technica l .1emoT:-1..ndum Ho . 860 13
schece nuct be enlnrged , RO thot nIl important conditiorts arc included.
3) The range of angle of attack : The minimum re sist~nce of ~ plan i ng surface falls betueon 4 0 and 6°. The fla~t system h~G the tende ncy to assume ~igh angl es of attack (un to ~ ~ 100) ut maxi mum resistance, and rr ith in crc~sing spee d to drop to smal l anglos as the result of tho bac~ rr ~rd shifting of th9 r csu lt ~ nt water force . To L1S1.lrC a s h ort ta"ko- off , it is pulled up before g et- away to a hi ~~ est possible an _ Ie . From th is it follows that in th o re g ion of maximum resistance the angles of from 5 ° to 11 0 ~n ~ - i n t~c s u cce edi ng st:-1..ge up to got - array - tho 0 an~los of fron 3 to gO must be i nvostignted; steps of 2° e~ch are, in Gener nl, sufficient .
Presentation of the Result s
EQ..r.!ILQi_ilQIT .- As n.n example, the test :ooints for DVL model 7 at ~ = 7 0 constant are giv en i n fi g ure 15 in the form
The points arc so 7e ll identifi ed in the accompanying leg end that the characterization of the developnent of the floTI ove r the model c an be obtai ned f~oD them .
Rcsi.9.1~n~ sL!1!Ht . !;:tQm.Q.g1 .- The resul ts are g iven in fir; .... ure 16 in nond i mensional for~ :
t = W a nd A c rah
n g ainst with the p a rame t e r A C a I = 'Y b :3 st whereby the moment Mst ' ro~crre d to tho k e el at the step c~n be co~put o d f r o~ tho n OD e nts obtai~od in tho test . T~l j 8 ul'cccnto,t i on ~'.. f fo rcls, o n tho basis of FFoudo f s Ian of 14 N.A . C.A. Tochnica l Mcnorandum No . ,860
~odo l sinilitude, n poss i b ility of conparison TI i th the r e sult s f r an o thor Dodols: I f ono i n~g i nes that the nodels to be cODp~red a r e a ll enlar ged to ~ un i t bean , the speed v fo r oqunl Fr ou do nunbor F is tho sarlO , .':\.nd fo r equ~ l l o~d coofficient ca l , the lift A is likewise the sano , so thnt tho g li de nUDbe r G E and the nonent c oeffi ciento Cnh ere d ire c t l y conparable .
Plotting € = f(a) separat e ly with F as the pa r amo ~ ter fo r Ca l BS the curve constant , f i gu re 17 g ives wi th c a r as the parameto r a curve of aopt , fo r which the co r r espondi ng E i s a min i mum .
Q.QIliQK_Qf_:QJdQ.Y u l1..Q.;Y: __.G:Q.\=L}Y£1iQK._li!.HLQ,l_KQ.§.jL • - The i n i - tial attitude of the float system fo r any loads a nd any position of the c ent e r of g r a vi ty , i s deter min ed f r om f i gure 18 who r e , i n nondime nsional fo r m, tho horizontal distance 1st of the center of buoyancy 0 f ro m the D step n~d tho ve rtica l d i stanc e of the water line nbove the k eel nt tho step tst i s g iven as a funct ion of a wi th c n ' ~s the parameter .
I nte r po l at i on of tho Resul ts
The scope of poss i b l e app licat ion of the exper i me n tal data is 'increased if freedom exists in the c ho i ce of l ength- beam r atio an d angl e of deed ri se within the r a n ge of the families of floats i nvest i gate d; i . e ., if by i n t erpolation of the test data the measurement s a re equally applicable to desi gn s wi th i n t e r med i ate va luos of tL/ b~t and ~ . F i gures 19 and 20 show ' fo r a ll s ix mode ls at a ~ gO € and cmh = feF) and at aopt Em in = f( F) a se ri es of loads correspondi ng to a normal float sys t em , wh ich is g iven by c I = C ' (1 - · 0 . 0 1 F2) au' c I = 1.70, thus a a o a o including all the mode ls .
The curves of the floats of one fami l y as wo ll as the corr e l ated floats of both families man i fest such a simila r cour se whil e the d i ffe r enc es a r e sO small that the appli c at i on of the re sul ts to i ntermedi a t e values by linoa r in terpolation i s justified . R.A . C. A. Technic~ l ~emorandUm No . 860 15
VI I. APPL I CATION OF THE RESULTS
Choice of Di mens i ons
With the size of the float a pp ro x ima tely determined from design re~u i rements , the oeam also is determined. A change in dimensions with regar d to take-off resistanc e is usually possible only uithin narrow limit s . A control is set up accordinG to t h e diagram (fig . 21).
At thr ee critical s p eeds : for instance, at maximum renistance , a t 0 . 6 v s t ar t, and 0 . 85 v s t a rt' E io plotted mrom the opt i mum shee t as f(ca ' ) (at maximum resistance the env elope curVG is taken from the max ima of diffe r ent load stages and used with a modium Froude number). Th e hydrodynam ic J.oad A+ and tho air drag W must bo doter mined approximately for the particular speed stages . It is then pos sible fro~ the E values of tho above figure to Give ~ rough course of the wat e r resistance and a lso of the tot ~l resistance, ae in figure 22 , fo r any bea n that may be of interest, from w ~ i ch a suitable bea n c~n f inally be definitely de t e rmined . The length is checked oy repe tition for differ e~t values of t L/bst "
Coordination of Wings a nd Float
The p roblem is so to cho ose the angle of setting rr 1 b e tueen u ing chord and pla ning bottom that the take-off occurs~t mininum resistance . The bost setting at the thr oe speed stages na med is determined according to fig~ ure 23. Fo r v = constant (0 . 85 Vs tart' for example), we plot o..go.ins t the angle of ~ tto.c"k of the \7ing (1,.
The ne rodyn~nic lift A Qnd the hydrodynQmic lift i !2 T:hich A+ == G - A:
,+ == Thon C .:t Tho corres~onding and ci,+ for this C 1+ curve a rc obtaine d fron the opt i num opt a sheet. Fran th i s tho vnt o r resistance W+ = Eain A+ is deternincd .
\Tilen the n.i r re::;istancc W i s de termine d, "\7e have 16 N.A.C.A. Techni c a l Memorandum No . 860
the totD-l :::: w+ re s i stan ce of Wtota l + W. I f the mi n i mur.1 of thi s \711 o,+ 0,+2 lies , say , at 0, 1 , fo r i ch opt = then + 0- 1 = 0,1 - 0, 2 The degree of f r eedom to diverge from 0- for do- l opt s i gn re~SQns , depends upon whether the total-res i stance curve is flat or reveals a di stinct mini mum . The best settinG in the upper speed range is usually qu i te c onstant ,
but diverges from it more or less at max i mum , so that 0- 1 mU3t be averiged .
Position of ~enter of Gravity Equilibrium of Mo ments
For the temporary c ente r-of- gr ~vity posit i on assumed i n the design, we establish , according to f i gur e 24 , for a sufficient number of speed stages the equi l i brium of the moments between hydrodynami c and aero dynamic total moment ( with the mos t exact poss i ble con o i derat i on of the slip stream effo ct and g r ound effect ) fo r take- off with n eu tra l clevD-to r and fo r naxi mum pos i t ive and negative ele vator deflection .
In tho speed rango b e tw e en maximum resi stance end about 0 . 85!~t~ ~t the a irpl~ne shoul d have the lowest pos- sible totnl resistance wi thout e l evator operation; i. e ., should t~ke o ff wi th neutral elevator . At max i mum re sict ancc i t se 1 f , "p ush i ng dOTIn II is usunl l y n e co s sar y , and i n the upper speed r ange, of course, nn increasing pull- up . If the c nlculation does not g i ve this des ired behavior for the pos i t ion of the cent e r of g ravity i n i t ially as sumed, the center of g rnvity must be shifted relative to the step nnd the calculD-t ion repeated.
On tho basis of tho curves of tho temporar y total ro sistance fo r take - off wi th neut ral el~vator and with max imum posi t ive and negative elevato r deflection , a take-off specification can now be set u p cove ring tho movement of the elevator fo r i nsur i ng the best take - off . ·
I _____.J I N.A.C.A. Technical Memorandum No . 860 17
VIII. COMPARISON OF THE DVL STANDARD FLOAT*
WITH THE A.A.C.A. MODEL NO. 35
From the many fo r eign float designs on wh ich mode l t est data are availabl e , the N.A . C. A. model No . 35 (ref erence 7) stands out for its goo d resi stance cha ract eris tics. ~ i b urc 25 g i ves the result o f a comp~r~tivc test; € = f(F) i s p lott e d wi t h ~ as the parameter. Both mod- e l s h ave tho s ame length , beam , and dead rise, and were t o'llod '7 i th the same l oad schedule simulating unloading -by wi.ngs.
The comparison shows that, at maz i r um ' re s istance, the best rccistance of the N.A. C. A. float at ~ = 7 ° i s 3 per cont ~OSR , but that at the highe r anglos a~ uhi ch a float at maxiouD res i stan ce a ctually runs , it i s considerably wors ~ ; thct is, by 1 3 p e rc e nt at ~ = g O , and 15 perceLt at ~ = 110. In p ure p lening c ondition the N.A. C.A. nodel is considerably i n f e rio r a t al l anGl os , which cen only bo ascribed to the unfavorable fo r m e ivon to ilie prosnure area by the po inted s tep . The resi stance curves do not cross u nti l spocds s h o rtly b efo r e g e t-auay, uhe r e t he coall, high aft e rbody surface o f t~ e N.A. C. A. node l c an i nflu ence tho resistance f avo r a bly because of le ss wett i ng . Whilo t~o standard ·flo a t yet allousa 7 0 s etting nnd only runs on t~c aft e rbody a t g O , tho N . A. C. A. float ~lready runs on tho aft e r bo dy at 7 0 - B c ondition TI~ i ch at got - auay c .'J.n only be r ealizod by havL1g l argo c ont r o l sur fO-ce DO ~ me nts available . The ge t - auay s pee d of the J .A.C.A. float Dust the refore be se t h i g h e r than the ctandard float . The N. A.C.A. f loat also shows a CO l s i derab1y more unfavor able suray pattern on a ccoun t of the absence of recurva tur e at the chine .
I X. FINAL RE ~ ARKS
The purpose of the development of a g ood typo of floa~ has boe~ n tta ined, as the above and othe r co ~pa ri sons shoTI . The making of tho l ar60 numbe r of tests that uere necossary to ma ke the float genera lly applicable was the re fore 70rth-wh ile. However, i t is ~ ot asserted that the float u il1 also s how the best characteristic s in all dimensions and conditions o f l o ad . (C f . re qu ire ~en ts under d), p . 4 . ) Tosts u ith dynamicall y similar mo de l s capable *Fro m tho fam ily C wi th t = 1500 in cour se of in vesti~a tiol1 . 18 N.A . C . A. Technical Memorandum No . 860 of flying are i n progress so as to ascertain these charac teristics also for the total range of the standard float, since English experiments (reference 8) have proved the feaaibility of such tests ~nd their extension to full size .
As an example of tho application of the standard float, figure 26 shows tho Ha 139, a four- engine twin floCl.t se[tJ~ lan0 built by the Hamburg Airplane Corpor~tion for the Luft Ransa , which is noted for its vory short tnkc-off time and pleasing t a ke- off and landing charact e r istics .
Transl~tion by J . A. Vani e r, N[ttion~l Advisory Committee for Acrono..utics. ~------~~--~----
N.A . C.A. Techni c al Memorandum No. 860 19
REFEREN CES
II 1. Sottorf : Veroffentlichung in Vorbereitun~.
2. Mewes, E .: The ' I Il1pact on Floats or Hulls During Land ing as Affected by Bo ttom Wi dth. T.M. No. 811, N.A . C. A., 1936 .
3. Sottorf, W ~: Expe riments wi th Planirrg Surfaces. No. 661 , N. A. C.A., 1 932 .
Sottorf, W.: Experime nt s wi th Planing Surfaces. T. M. ~~ o. 739 , N. A. C • A., 1 934 .
4. Mewes , E.: Die St o ssk r ~fte an Seeflugzeugen bei Starts und Landungen . VLF-Ja h rbuch 1935 . I 5. Seewal~, F .: On Float~ and Float Tests. T.M. No. J J 639, N. A. C. A., 1931 . I J Shoomaker, James M., and Pa r kinson , John B.: A Com I J p lete Tank Test of a 10del of a Flying-Boat Hull - J J N.A.C . A. Model No . 11. T. N. No . 464, N.A.C.A., 1933. I 7. Shoemaker, James M., and Bell, Joe W. : Completo Tank IJ Tests of Two Fl ying- Boat Hulls with Pointed Steps - R.A.C . A. Models 22-A and 35 . T. N. No. 504, N.A.C.A., I 1934. J 8. Coombes, L . P., Perr i ng , W. G. A. , and Johnston, L.: I The Use of , Dynam icall y S i mi lar Models for Deter mining the Porpoising Char acteristics of Seaplanes.
IJ R. & M. No . 171 8, Briti sh A. R. C., 1935. I 1 Perring, w. G ~ A., and Hu tch i nson, J . L.: Full Scale I and Model Porpo i s i ng Tests of Si ngapore IIC. I R. & M. No. 1 712 , Bri t i sh A. R. C. , 1936. J J I J J J J J I I i I i
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N.A.C.A. Technical Memorandum No. 860 Figs. 1,3,4 - Lt i qo I c.'~ 6,0 1 ~i',bsl + Flying boofs 'IQ'I~~ Y 0.38/1 5,0 bst J- 7}jJ x-- qso • Twin flo of seopkmeI(o.rrf(ulz) {loot _ -,- 410'CKIJv~ f..-,' ~ -I f 0 ide ~oi -~ J!lP1 rtJ7?d- ___ 100- rhe !-;;~N'f Iffo~J... ffo1!lf '1/1 orltnf!.osletpif(!- ISO (' W;. -"¥ YI1'If6J11br1Oftl!lfq+ - IlllTlf/lfft, -- ~ 100 0 .1 r.--: Nuco!'&:,/, __ , + JtkorJ:% W_ ' I-:::::t:::;:;:: t§:0- § HSJl.Hom-flHo./I f!1f'!Jr~f' _,.J- JihgrJ: rJfz~t:--..... P- z 1=f= --(Tf;~ An/Om:M:lIJ'Ar~ __ ~ z,o e-r--- f-- , atp«q, 'lJPl-fom-Au8,;;;;;---:( ---::::: ' Do'v§IOJJa'P.,!!n~ ~1""-~:tW'- +~~i:r I:: ., ,.: ....1---.:.--' .-A.,---~, - r--~ 1 b.. t ,If) i' I- ~l.1f~' '-1~~.I'~~~Sl~j p::iOjfQ 'II ffo"_/ , - '"':' ~ , ----d., /frOP ,.-...-.JtPb~ \ jne.!.Q!!!--;/2d}",- to II 1-" N!:F;;orl !§!3 ~, 1-: ~ ~t:~ ~ qa kf ll!Jt;}ff6.. tI "'-+';"'-llfJ/~~" 8e0Jfl 52 fupermorlneSDB ;/101 /ff}!.9 - J) '1'1 cro'raui r 'Supermorlne- SS ~ v;~.:§fr""" pSopwil!l ~ !,9{f
D,J ~ 1=~ qz 1= 1= 1= I='l- I- 1-'1 • I II t1 ul 11111111 I1II IJlllllll 11111l 1'1111,", 111111, ;, ~ ~ Jlui llll.JJ.l ",I" 11111, ""1,"1,,,. 0; qz 0,3 0,11 qs q8 qa rO 2,0 ),0 _ '1,0 5,0 qO ~O 10 zo 3(1 If 0 Sf} 80 80 !l .or !lIz ill 1017:> Figure 1.- Beam at step of various airplanes against gross weight.
rorehotlyalone Propeller --x thrust $ I I ,.' -+--. Lock ofS'vpporf from offerbc& I 'r I / / ' Ii ' / <., ",- !l:: 'd
--1---- III ----1-- Figure 3.- Take-off diagram.
AI' .4' d AI
WH Figure 4.- Flow paths and forces ai stage I. W.A.C.A. Te chnical Memorandum No. 860 Fi g. 2
Junkers Ju 52 6/).'.51o.C;·2.05
Heinkel He59 6~'~ISIo.Co-1.89
s===;d;;;>:=~ f nglOnd: 810ckIJum Perin m G-1~.75fO. '~ ·O.268
Snort Calcvlla E;;-F?: 6' '0.2'0.c,;-0.J6
Snort Empire c-· ~gure2.- a·I8.35Io. <,;.0.6.5 Domest i c and f orei gn float U.S.A.: systems . . WevstOl1e(/lAVYPHBJ shown ~ G .6.810.r:,,··~22'1 f or
1 ton SlkorsJ VOughl Corsair 6-2.3810. <;;-'.79 France 81ertOl5190 6-221•. <;; -o.~7 ~--t=- Sora Cloud 6.J.8510 . ...·0 .12 LeO 257 GI2-+.J5to.c,;-1.00 "'''' __,'''',,.'-- --',z.. Scale Italy Savala SS5 .% -~.OID. c.; - o.~ L N.A.C.A. Technical Memorandum No. 860 Figs. 5,8,9,10.11 recvr ved chine section [ -~~~!,~~, d7777/i0::::. - .- --- ~I Figure 8.- Impact load \ ~ PreSSLlre r:liagrom factor against \ f beam of float . \ I V Figure 9.- Diagram showing different curvatures of the fore body. 16 It' oWExomple 'Osl'f3 const , Ca .qG6 Spray fhrown o.Jt f ~J$ . / -===::: ~idewny " by a ~ 900 - ~160'I N'O' 12'0· tUU' .~~/ Di h edral anqle of dead rise t ~ VL IY load ossvnrpfion 1 .1 I ...... "" ~ 'y-- "~ c~~/ ~ v._ ~ ~ 60 Figure 10.- Resi stance and impact ~igure 11.- Effect of form force against included of section on angle of dead risa. deflection of spray_ N.A.C.A. Technical Memorandum No. 860 Figs. 6,7,12,26 Figures 6,7.- Comparison of spray of model 0.2 va (bat 0.2m) and 0.4 VH (bat 0.4m) at the same load 18 kg; speed 6 mis, trim 6 deg. Figure 12.- Deflection of spraYi left half: form of section according to figure 11c, right It \I II II " ,,1\ lIb. Figure 26.- Ha 139 built by the Hamburg airplane Co. for the Lufthansa. l 42511---1---1-----r----,------~ ~ -, ·>- l'-f // ---- "'-, -\ • / , /' o / \ 4201 "" I 7'"",'- =-=---,1:,,;£ \ ·> ·8 \ Figure 13.- Effect of depth of tb () step and angle of g 4151 ", ....:~n afterbody on the resistance. .... I~ () ~ r-' s: :II 410 .. (),f ~ 405 ,,/ -...-~~~--~ " d,Of6& " ~ .. {) " g 405] r- -..... p o~ • (X) , I 01 I I V fI-I S ~ oI ~ .J .r;.-::;r;;r- o " rg'~ Il""'''''' ~ '''''''''!I ~ - OV/la ~ Dna • o~_~ ...-=: ,=,- ~ >~ 1- -- ' .I', i. ~~.:;.,~~~ I Z' ' ~:2-, ' ~ - ----~."" " ~'r" .jJJJ .j.¥Z4, #,1)1 '1'11.. , ~'J6" Figure 14.- Plans 11""'=<,""" " " , , ...... ,~.", ... ~~~~ OY/T7 1 PYlY8 OYL19 ~ of - '7 ,' I -- DVL standard Fc"'·;;;,,- -- .... ,/ - -=--~..-:,; .-._""" ~----6./-----l t r -~ ~...... -~ floats. family A +=- ~ "",ii, B-on 'l,J8U,,{{·t»~ II j I i I I ~ (DVL la, 7 and 1:,m:: f " ~ 8) and family ...... ~ ..,.,."'" ~~ ( 1 ) ~ ,-""",~ 1>t:B DVI, 17,18,9 • ~ ''''''''''''''~ ;;? ~<:> .... /-- ~ (JIj ."", ,'; "o'~ ... ,/ oQl... fE: :..~...;.»»> ~ ~~- ~ "-...~~ 'h" ~ 5'" ·~ Fro, ) J r I) IS 11 8 /. ,11 lJ .II I CN $~Clirlon " t" . • l j ., 1 " /j -lJ ,:5 OY/8." I r. J 0 II 17 Pn J'II J , j , I /I " Jj " ., " l> tJ ,II /7 Y r-' " ~ • Side and bottom of float wetted- buoyant condition !;tl ·•>- As above. Forebody wetted whole length. A blister of water C') appears at the bow (limit of load). ·>- • • ..;i ~·7ccns Left half of circle sides clear forward only, wet most of length. CD ~ 8 OC o ~Q Condition on s1de8. 2JJ g .... 8 84 ~ OC o 1- ~ :}In stages I and II sides mostly clear, only wet a little, lit 2.4 i mostly in way of step...... II:: 84 ~ OC ~O ~ 2.0 () Right half of circle afterbody bottom hard on water, more than o '"1 8j ~ ~O OC 0 1/2 length of afterbody ~ f~~I G Condition on bottom afterbody bottom on water les8 hard, ~Gl:ip::o OC o I!J. les8 than 1/4 of afterbo~ ~ Q C I :tZ a 27 0,27 ~IIIIIIIIIIIIrlllll~~~11111111$11111r\r , A It ~~ / Ca,- r-lJlt 23 ~ :'0. / 0,23 :r; Z 7/1 i:IIIIIIIIIII_WHmlll~ln: a19 ~~ 0,19 ...- - ,'18 - b ,11 0.15. o,tf 415111111111f:r111IFI{il~~MtIIIIIW5 ~ 0. 11 0,11 410' 'J4 , , , , I I , , , , , , I I I I I I I I , , , , , , I , I , , , I , I IqifJ t'!I ~""" CIl Figure 16.- Resistance and moments; example Figure 17.- Optimum resistance and the I-' for DVL 7. cx.=7 0 const. corresponding trim (best trim). O'l I-' ...:J 2: ·~ ·o q8j ~ ·~ ~ • ~ 1 1 1 1 I 1 1 .... o ", ' I ~ ~ IT:. ~ .", Ie n N -~o ~~~_l..:=Jt- ~\ g' ~ ~ , J .... .t II 41 ~ n \. l ' -, l lit ~ ~nd~"f(" ," gSI "if ..... ~ 14""~- ~"+I " J!:: " ~ ast~; ~ 1\\ '\ ',s ". 4' , tv p -10 0 '''' "'" .. ~ v ~ ~ I-~ , q.; ~,l'.ct.- '" ~ ~ '-'"~ 1" I- 1-10>- ~ rv L.-l- F"' i 4111 1- I~~ k- ~ 14- ~ ~ ~ ~ ""~ . ~ L.- \ (X) ..."' ... o UI ...- " 0 g; ~ l.--'-- .,'\ q S If ~ - "'- I'\. ~ 4 '--'-JIi6d us _ I- I' ~" ~ J..-i-"' qJQ l...- i£:: -I--- "\ ~ t" 14 Figure 18.- Poaition of center of buoyancy 0n and water q line ageinst load trim. Example for DVL 7 model. ' (~----,-----.------r-----.------r-----~----~~UL Qll ------1f--.-----II---~.... Qzo---f--.----I- alf--~r-7;+-t7'~--+-----f--=:::""-!~;,;;,::::"'+=------I-----~ // /'/ {/' /// /t /' 0'0 ---,'-1------t-----+-----+------+-----1------I------1 qll ---j------t------+----L-----+------~----l------~ ,._v_ YiT,/ J Figure 20.- Optimum resistance for ell models at the same load. qB5 ' Y Ge/'o'WC1'y "10'" Getawoy II' I/U V ,, y cons! 6 I d- oe!.. -- _L_-=-=ic:(.'f- I _--- Figure 23.- Determination t i of angle betwee"n wing and planing bottom. N.A.C.A. Technlc~l Memorandum No. 860 Figs. 24,25 v· cons!. Figure 24.- Equilibrium of moments. --- NACAJS f------~-8,JSbJ't - - OVL- Stondord Floor r---~~---r---+---r----~----r----1q~ ~~-~----J~---~Q---S7---~D~--~7---~84~ if- V -ygooJ't Figure 25.- Comparison of DVL standard floats with the N.A.C.A. model No. 35.